#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>

void err_sys(const char* x) { perror(x); exit(1); }

void upper(char *s) { while((*s = toupper(*s))) ++s; }

void filter(int input, int output)
{
    char buff[1024];
    bzero(buff, sizeof(buff));
    size_t n = read(input, buff, sizeof(buff));

    printf("process %ld: got '%s'\n", (long) getpid(), buff);

    upper(buff);
    write(output, buff, strlen(buff));
}

void filter2(int input, int output)
{
    if (dup2(input, 0) != 0) err_sys("dup2(input, 0)");
    if (dup2(output, 1) != 1) err_sys("dup2(output, 1)");
    execlp("/usr/bin/tr", "tr", "[a-z]", "[A-Z]" , (char*)0);
}

int main(int argc, char** argv)
{
    int pipe1[2];
    int pipe2[2];
    if (pipe(pipe1) < 0) err_sys("pipe1");
    if (pipe(pipe2) < 0) err_sys("pipe2");

    pid_t pid;
    if ((pid = fork()) < 0) err_sys("fork");
    else if (pid > 0)
    {
        close(pipe1[0]);
        close(pipe2[1]);
        char* s = "Hello there, can you please uppercase this and send it back to me? Thank you!";
		write(pipe1[1], s, strlen(s));
		close(pipe1[1]);

        char buff[1024];
        bzero(buff, sizeof(buff));
        size_t n = read(pipe2[0], buff, sizeof(buff));
        pid_t mypid = getpid();
        printf("process %ld: got '%s'\n", (long) mypid, buff);
    } else
    {   // Child.
        close(pipe1[1]);
        close(pipe2[0]);

        filter(pipe1[0], pipe2[1]);
        //filter2(pipe1[0], pipe2[1]);  // FIXME: This doesn't work
    }
    return 0;
}